body {
  background-color: green;
  font-size: 14px;
}
.box {
  background-color: green;
}
.box::before {
  content: "这是一个双伪元素";
  display: block;
  width: 200px;
  height: 100px;
  background-color: red;
}
.box a {
  flex-direction: none;
  font-size: 14px;
}
.box a:hover {
  color: green;
}
